Background: The triplet regimen of S-1, leucovorin, oxaliplatin and gemcitabine (SLOG) has shown promising efficacy for metastatic pancreatic ductal adenocarcinoma (PDAC) in our previous study. Current multicenter randomized, phase II study compared the efficacy and safety of SLOG versus modified FOLFIRINOX (mFOLFIRINOX) in patients with advanced/metastatic PDAC. Methods: Patients with chemo-naïve, histologically confirmed advanced/metastatic PDAC, were randomly assigned to either SLOG (gemcitabine 800 mg/m², fixed-rate infusion and oxaliplatin 85 mg/m² on day 1, plus daily 40/50/60 mg of S-1 based on BSA and 30 mg of oral leucovorin, twice daily, on days 1-7, every 2 weeks) or mFOLFIRINOX (oxaliplatin 85 mg/m², irinotecan 150 mg/m² and leucovorin 400 mg/m² on day 1 plus 5-FU 2400 mg/m² for 46 hrs, every 2 weeks). Patients were stratified according to disease extent, ECOG PS and primary tumor location. The primary endpoint was 6-month progression-free survival (PFS) rate. The secondary endpoints were objective response rate (ORR), disease control rate (DCR), PFS, and overall survival (OS) and safety profile. Tumor response was assessed by CT/MRI every 8 weeks according to RECIST v1.1. As an exploratory trial, 130 (65 per arm) patients were estimated to detect a two-sided 15% difference in 6-month PFS (60% in SLOG and 45% in mFOLFIRINOX) with a significant level of α = 0.1 and β = 0.25. Results: Between March 2018 and October 2019, 130 patients were accrued. One patient who was assigned to mFOLFIRINOX arm didn’t receive assigned treatment. Of them, 62.3% were male, 45.4% were ECOG PS0, 81.5% had metastatic diseases, and 16.9% had prior surgery. The 6-month PFS rate was 55.4% in SLOG arm (n = 65) and 50% in mFOLFIRINOX arm (n = 64) (p = 0.850). The ORR and DCR in the SLOG and the mFOLFIRINOX arms were 40% versus 26.6% (p = 0.135) and 76.2% versus 71.9% (p = 0.550), respectively. The median PFS was 7.5 months in SLOG arm and 6.5 months in mFOLFIRINOX arm (p = 0.395); while the median OS was 12.9 months in SLOG arm and 12.1 months in mFOLFIRINOX arm (p = 0.88). Ten patients underwent conversion surgery, of whom 7 had SLOG and 3 had mFOLFIRINOX. The incidence of grade 3/4 neutropenia was significantly higher in mFOLFIRINOX arm (53.2% vs. 16.9% in SLOG arm, p < 0.0001). Conclusions: SLOG could achieve comparable but numerically better ORR, and median PFS and OS as compared to mFOLFIRINOX in patients of advanced PDAC. SLOG can be an alternative first-line regimen for advanced PDAC patients. Clinical trial information: NCT03443492